Mixing OpenGL and Quick Controls lead to drawing errors in TextField

Steps to reproduce:
1.) Open the attached example and run it.
2.) In the top left corner there is a popup element with a TextField in it but the text field is not correctly drawn (i.e. the line indicator is missing).
3.) Replace the SquircleRenderer::paint() with

void SquircleRenderer::paint()
{
  return;
}

Now the TextField is correctly drawn.

I have tested this on Windows and Android.

The problem does not occur in Qt 6.2.1. It seems as if one of the shaders used for drawing the TextField is not properly set (i.e. missing when the OpenGL state is reset) in Qt 5.15.*.